In the last years the rolled hair (also called the Frankenberger-hair or Pernix-hair) with very good response at low temperatures has been used at the humidity sensing element in the German morse-radiosonde. In two papers SCHULZE (1952) shows from measurements made at Flensburg how extremely useful the new method is in measuring humidity. The time-constant of the rolled hair hygrometer at normal temperatures is five times smaller than that of the unrolled hair and the hair is also functioning at as low temperatures as - 70° C, where the time constant is about 500 sec at 100 per cent humidity.DOI: 10.1111/j.2153-3490.1954.tb01134.x